Workload of a network has to be evenly distributed across multiple network resources (or network nodes) in order to optimize the resource use and throughput and avoid overloading any of the network nodes. In a network with numerous nodes, there may be hundreds or thousands of active sessions at a time. Load balancing and traffic dispatching for these networks require ensuring that incoming packets for an ongoing session are forwarded to the same node that has been processing the session's previous packets.
In addition, scaling events require traffic stickiness to ensure that packets for ongoing sessions are still dispatched to the same nodes that were processing the sessions prior to the scaling event. For instance, adding a network node requires ensuring that packets belonging to sessions that existed prior to adding the network node are dispatched to the same nodes that were processing the existing sessions. Similarly, scheduled removal of a network node requires stopping the dispatch of packets for new sessions to the node and ensuring that all ongoing sessions processed by the node are over prior to removing of the node.
In a network with hundreds or thousands of ongoing sessions, a stateful system or appliance (such as stateful load-balancer) is not able to support scale-out traffic dispatching due to the system resource limitation, such as the amount of memory required for storing stateful information. The pure hashing algorithms can support large amount of scale-out nodes, but do not support traffic stickiness well.